[R-sig-Geo] polygon over or intersect with more than 2 files/layers

[Roger Bivand]

On Thu, 31 May 2018, Bannar-Martin, Katherine wrote:

> Hi,
>
> I've had no success at finding a tool in an R package that can calculate 
> the intersection/overlap of polygons for more than 2 layers.
>
> e.g. 
> plot(st_intersection(st_union(LateYear2008),st_union(LateYear2009),st_union(LateYear2010),st_union(LateYear2011),st_union(LateYear2012), 
> st_union(LateYear2013),st_union(LateYear2014),st_union(LateYear2015),st_union(LateYear2016),st_union(LateYear2017)), 
> col = 'red',xlim=c(min(d$x),max(d$x)),ylim=c(min(d$y),max(d$y)),axes = 
> TRUE) does NOT work.

Why would you think it might, given that the help page only shows pairs of 
objects? The underlying code in GEOS is for binary operations. GRASS also 
handles binary overlay, and the same applies to PostGIS.

It might be possible to work out intersection candidates by building trees 
of envelopes and querying multiple layers based on non-zero envelope 
intersection, but

>
> Does anyone have any suggestions? Is there a way to save a shapefile 
> with multiple layers of polygons and then run an over/intersection tool.
>

No, a "shapefile" has one layer only, unless you want a folder with 
multiple shapefiles. GPKG can take multiple layers, but it isn't obvious 
why this would help.

> I can run each pair-wise overlap between layers in a loop but the number 
> of combinations is long.

Obviously. If you have to have vector, you have to do this pairwise. If 
raster is an option, probably there are many more possibilities; GRASS 
r.cross takes multiple raster layers for example.

>
> Efficient solutions welcomed.

  ... and code contributions ??

Roger

>
> Thanks!
> Katherine
>
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>
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-- 
Roger Bivand
Department of Economics, Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; e-mail: Roger.Bivand using nhh.no
http://orcid.org/0000-0003-2392-6140
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